Process of protecting underground metallic surfaces



peratures, the pitch will Patent ed July 14,, 1936 Process or morso'rmam smrsmc soar-sons Clarence n. Eckert,

Englewood, N. 1., assignor to The Barrett Company, New York, N. Y acorporation of New Jersey No-nrawing. Application January 21', 1935.

Serial No.

z (o1. iii- 10) This invention relates to a method of protecting metalsurfaces adapted to be placed underground so that corrosion of thesurface is inhibit ed, the method involving application of the micapitch composition disclosed in my co-pending application Serial No.475,839 filed August 16, 1930, and in application Serial No. 334,608filed January 23, 1929, the latter application having issued as PatentNo. 1,773,131 on August-19, 1930.

As disclosed in my co-pending application, one object of my invention isto provide a toughened pitch composition which will the highesttemperatures encountered in use and, on the other hand, will not breakor shatter at low temperatures which may times. Coal tar and oil tarpitches have heretofore been used for coating and surfacing but presentthe difliculty that if the melting point of the pitch is madesufliciently high to overcome flow when exposed to maximum summertemwhen exposed tolow temperatures, 1. e., winter temperatures.According to the Manhayfer Patent No. 1,112,817 of October 6,, 1914, thesurfacing and coating properties of pitch are improved by interminglinginfusorial earth of kieselguhr therewith in such quantities andproportions as to render the'finished product plastic. Infusorial earth,it has been found, clings together in. lumps and it is diflicult tohomogeneously disperse it in the pitch. When dispersed it readilysettles out of the pitch upon melting of the pitch-infusorial' earthmixture. Due to the physical structure of the infusorial earth, itserves merely as a filler and does not substantially increase thetensile strength, of the coating resultingfrom the application ofinfusorial earth-pitch mixtures to the surface to be protected. In otherwords, the effect of the infusorial earth on the pitch is com.- parableto the effect of a stone ag regate incorporated in concrete on theconcrete, 1. e... it increases the compressive strength but does notmaterially increase the tensile strength of the concrete.

According to my invention, mica is mixed'with pitch to produce atoughened-pitch composition. Mica is less expensive" than infusorialearth. does not cause foaming when mixed with pitch, remains insuspension without 5n appreciable tendency to settle out, is flaky instructure and not bleed or run at be encountered at be excessivelybrittle has greattensile strength so thatwhen admixed.

with pitch it impartsbinding strength to the mixthereof at lowtemperatures. Due to the leaf.

like structure of mica it greatly increases the =ture and thus preventsbreaking and shattering that-the mica-pitch composition can tensilestrength of the resultant coating. The eflect that mica has ofincreasing the tensile strength of the coating may be consideredanalogous to the eifect of reinforcing steel incorporated in concrete onthe concrete. Per unit of 5 mica in the mica pitch composition, ascompared with "spheroidaP fillers such as infusorial earth in earthpitch compositions, the surface of mica contacting with the pitch is fargreater and hence far greater reenforcement is obtained by incor- 10porating mica in pitch. Due to the increased reenforcement obtained bythe use of mica less mica than infusorial earth is required to produce acomposition resulting in a coating of desired strength. Hence, for agiven strength coating the mica pitch composition contains less micafiller than the infusorial earth filler, and the mica pitch iscorrespondingly more fluid at any temperature above its melting pointthan an earth .fllled composition. It follows, therefore, be appliedsatisfactorily at lower temperatures. Hence, less evaporation ofvolatile content from thecomposition takes place. Furthermore the pitchcontent of 'the coating is the important protective 25 agent. 'With micapitch compositions more pitch is present for each pound of compositionor unit of thickness of coating produced thereby and, hence, the surfacecovered with the with pitch to form this improved composition. I

have found that satisfactory and improved results may be obtained with aground white mica the following mesh composition: 40

' Per cent Retained on 28 mesh 0.1 Passing 28 mesh retained on 48 mesh13.8 Passing 48 mesh retained on mesh 11.2 Passing 60 meshretained onmesh 11.7 415 Passing 80 mesh retained on mesh"... 13.0 Passing 100 meshretained on mesh. 10.9 Passing .150 mesh retained on 200 mesh 6.5

200 mesh... .31. 8 Loss 1 1,0 60

Tota 100:0

' The mica of the above mesh composition is known as No. 80 mica.

' corporated in pitch raises the melting point a;

ing from 10 to 30 per cent mica thereto, agitating the pitch whileadding the mica. and agitating the mixture of pitch and mica. preferablyby a suitable mechanical agitator or stirrer until a substantiallyhomogeneous mixture of pitch and mipa is formed. It will be noted thatthe resultant mixture is made by admixing a major proportion of pitchwith a minor proportion of mica, in the particular embodiment disclosed,10 to 30 per cent mica. A pitch of sufiiciently high initial meltingpoint to give a mixture of the desired melting point is of course usedas the starting pitch. A pitch of lower melting point may be distilledin the usual manner to remove distillate oils until the resultant pitchis of the desired melting point and then the resultant pitch may bemixed with mica of from to mesh to form the desired mica-pitchmixture. Ihave found bestos without deleteriously affecting the surfacing andcoating properties of the mixture. Preferably, however, mice. is used asthe sole filler for the pitch.

The following tabulated properties of micapitch compositions serve toemphasize the difi'erences between mica-pitch compositions andcorresponding untreated pitches:

It is evident from the foregoing that micainconsiderable extent, to wit,62 in the case of example 5 involving a paving pitch having a melt ingpoint of It; 21'' in the case of Example 6 involving a paving pitch; 24in the case of Exampie 7 involving a roofing pitch of the melting pointof 143 1". and having 18% mice incorporatprepared by first melting thepitch and then addthat a part of the mica may be replaced by as- Meltingfi Composition point pitch mixture a no use 4 71.5 a in? i? sud inExample Meltin int itch 7 Composition ga l m- 7 2 1 6 .4 mice.... }l25I. (known as 187 F-.. )6"

78.6 9 itch..- Davin pitch). 6 18 F. own as F... m"

pitch---.- paving pitch). 7 l8 0 mice 43 F. (known as 167 F... 134'"pitch.--.- roofin pitch). 8 mioa. }l43 F. %known as 187 F... H."pitch...-- oggoiiingkgitch). 180 F u U own as a 9 sam as). W

ed therein; 44 in the case of Example'8 involving a roofing pitch of 143F. melting point and. having 21% mica incorporated therein and 15 in thecase of Example 9 involving a water gas tar pitch having a melting pointof F. and having 20% mica admixed therewith. It will be noted that thephysical characteristics of the 'mica-pitch composition are dependentupon the particular pitch used and the amount of mica admixed therewith.Further, the preferred composition disclosed herein consists only of twoingredients, to wit, pitch and mica.

' As disclosed in my co-pending application,

the mica-pitch mixtures described herein have been found particularlyvaluable as a coating medium for pipe lines and metals generally toprevent corrosion. Pipe lines are particularly subject to corrosionunderground because of the electrolytic action of ground currents whichcause rapid deterioration of the pipe line in the field of the electriccurrent, particularly where the ground is moist or contains groundwater, as is frequently the case over long sections of pipe lines usedfor transporting oil and gas, and in the case of pipe lines in citieswhich are necessarily adjacent sewers and water lines. The

mica-pitch composition described herein, whenapplied as hereinbelowdescribed to form a smooth, uniform coating, acts to inhibit to aremarkable degree the corrosive action of ground currents on the metalsurfaces to which it is applied. I attribute this property of thecomposition to the insulating quality of the pitch and of the flatflakes of mica homogeneously distributed therein which form naethroughout the composition. the mica enhances the permeability to waterof the coating composition, the tendency of ground currents to followlines of moisture penetrating the composition is greatly reduced. Thisnon-permeability of the mica-pitch composition to moisture and groundcurrents with resulting corrosive action on the pipe line, is furtherminimized by reason of the smooth, glossy outer surface which is acharacteristic of my micar-pitch composition, which smooth outer surfacedoes not present irregular- Further, since insulating lamitensilestrength and nonities and rough spots constituting points of atapplyingto such surfaces a substantially 'uniform coatin my invention. This topipes or metals by dipping the pipes or metals after priming into a bathcontaining the micapitch mixture or by wiping or pouring the micapitchcomposition onto the material or article to be coated or by. any othersuitable means such as spraying and the like.

The property of the mica-pitch mixture to become freely fluid atelevated temperatures, 1. e., at temperatures somewhat above the meltingpoint of the mica-pitch mixture, renders the mixture 'as hereinaboveindicated particularly suitable for application to pipes or metals bydipping, wiping, pouring, or spraying processes. The mica-pitchcomposition .at temperatures below the melting point is substantiallysolid but upon being heated to ing point becomes freely'iluid, formingaliquid which is substantially homogeneous throughout and which I havefound is admirably suited for of the mica-pitch composition of purposesof coating or enameling metal.

somewhat above the meltcomposition may be applied As above iii dicated,in order to adequately 7o mica fillers for must wet the surface theenamel mustr be inous paint free of employed. Pitch 2,047,772" protectthe metal surface it is important that a smooth, substantially uniformcoating, 1. e., free from pits and openings and of substantially uniformthickness, be formed on the metal surface so that no portion thereof isexposed to soil conditions upon burial. I have found that the mica-pitchcomposition of 'my invention forms such coating somewhat above itsmelting point and such that the composition is freely fluid. Thetemperature of application of. the mica-pitch enamel should not begreater than 200- F. above its melting point. Thus, for the mica-pitchcomposition disclosed herein having a melting point, in round numbers,of from about 150 F. to 200 F., the maximum temperature at which theenamel is maintained during application should not be greater than about350 F. to about 400 F. By keeping the enamel within this temperaturerange its composition will not be radically changed, i. e., substantialevaporation of the oil content cf the pitch and substantialdecomposition of the pitch content with free carbon formation will nottake place. With other than pitch in order to produce a compositionwhich can be applied to pipe to form a uniform coating thereon, it wasfound necessary to heat the composition to such high temperatures "thatdegradation place.

To form a satisfactory coating, the enamel to be coated and bond withthe primer usually employed, anda certain degree of flow of the enamelmust take place be-v fore it-sets in order to permit the formation of asmooth even surface. To meet these conditions, above a certain minimumtemperature hereinabove pointed outwhen applied, so that prematuresetting of the enamel is avoided. As the primer for the, pipe 2;bitumilllers, free flowing and con. taining .a volatile solvent whichevaporates upon application of the primer to the pipe may be dissolvedin a solvent, which upon application, forms a thin coating with whichthe mica pitch composition bonds has been found a satisfactory primer.-

1 have found that an eminently satisfactory coating can be produced byapplying the micapitch enamel at a temperature at least about 125 F.above its melting point. 7 Thus, for micapitch enamels' herein disclosedhaving a melting point of from about 150 F. toabout 200 F., the minimumtemperature of the enamel during ap plication should be from about 275F. to about of the pitch took 325 F. respectively.- while the enamelmight a lower temperature than that be applied at herein indicated, forthe best results the temperature should be at least about 125 F. aboveits melting point. Q

(one possible theory which may provide an additional reason why optimumresults follow from 1 applying the enamel at the minimum tempera? planttime interval .ture indicated is as follows: In order to obtain aneffective coating it is important that the mica particles thereinbecoordinated with respectto' the surface of .the coating, e. g., the micaflakes be arranged parallel to the surface forming laminae whichreinforce the coating and improve the non-conducting qualities thereof.A ummust be'allowed between the time. of application of the enamel andthe time of setting for the mica particles to become properlycoordinated with respect to the surface. If the temperature ofapplication is below the optiapplying the enamel when applied at atemperature draining or spraying,

mum temperature specified the enamel will set before an opportunity isafforded the mica.

particles to become properly coordinated. By withinthe range speci. ed,i. e., for enamels having a melting point of om about 150 to about 200F. at a temperature of from about 325 to about 400 R, an opportunity isafiorded the mica particles to become properly coordinated with respectto the surface of the coating and a smooth, uniform, glossy coatingresults.

Whether the coating is ,applied' by dipping, it is important, as notedabove, that the temperature of the mica-pitch composition be maintainednot lower than that at which it will flow readily to produce a smooth,uniform coating. If to be dipped into. a bath of the enamel and thenremoved, the desired smooth, uniform, glossy coating in accordance withthis invention is produced by the excess enamel draining from the dippedpipe. If the temperature of the enamel the pipe to be protected is notdrain uniformly from the pipe but the excess enamel will set and hardenon the pipe, resulting in a coating of different thicknesses in whichweak spots appear. Likewise ifthe enamel is applied to the pipe bypouring it on while rotating the pipe and the temperature of the enamelis below the optimum minimum temperature hereinabove pointed out, theenamel may hot wet the pipe no! bond with the primer usually employedand will not flow over and uniformly coat the pipe but will set on thepipe during covering the complete surface thereof.

I have found that mica-pitch compositions, applied to pipe, whilemaintained at a temperature falling within the range hereinabove specified, result in a smooth, glossy, uniform coating through which the micaparticles are substantially uniformly distributed in the form oflaminae. The thickness of the coating will depend upon the particulartemperature of application of the enamel. For example, with an enamelhaving a melting point of about 200 F. and applied at a temperature ofabout 395 F., a coating approximately inch thick resulted. When thetemperature of application of this enamel was lowered to 335 F. acoating approximately a; inch thick resulted.

The melting point of the mica-pitch mixture herein given is determinedby the Ring and Ball Method, A. S. T. M. Standard Method 13-36-26.

While preferred embodiments of this invention have been described, itwill be, understood that this invention is not to be limited by thedisclosure herein but only by the scope of the appended claims.

I claim:

its rotation without 3 00 1. The method of coating metallic pipes whichcomprises applying in heat liquefied condition a composition constitutedof a major proportion of pitch and a minor proportion of finely dividedmica, said composition having a melting point of 5 from about 150 F. toabout 200 F., to the pipe condition at a temperature of from about 325F.

while the said composition is in heat liquefied to about 400 F., causingthe said compositiondn said heat liquefied condition to completely cover7 .the pipe and then set thereon to produce a comprises applying a p tcprime to: the P 1 575 applying in heat liquefied condition a,composition constituted of from 70 to 90 per cent coal tar pitch andfrom 10 to 30'per cent finely divided mica, said composition having a.melting-joint of from about 150 F; to'about 200 F. to the primed pipewhile the said composition is in-hea.t

liquefied condition at a temperature of from about 325 F. to about 400F., causing the said composition in said heat liquefied condition tocompletely cover the pipe and then set thereon to produce a. smooth,uniform coating covering the exterior of the pipe.

' CLARENCE R. ECKERT.

